U.S. Pat. No. 4,625,597 (Cast), issued Dec. 2, 1986 discloses a screw driving apparatus, wherein the drive motor is connected to a screwing unit including a guide head and a feed mechanism for feeding screws which are stored in a magazine. A handle is attached to the motor housing and extends essentially perpendicularly to the motor axis. German Patent Publication DE-OS 3,333,427 corresponds to said U.S. Patent No. 4,625,597 (Cast). In the known screw gun the drive motor is arranged centrally above the handle or even inside the handle. These known devices leave room for improvement with respect to the arrangement of components to obtain an optimal balance.
In other known screw driving devices the handle is arranged all the way at the end of the drive motor opposite the end connected to the screwing unit, whereby the center of gravity or balance point of the screw driving device is located at a considerable distance in front of the operator's hand which grips the handle. It is therefore almost impossible to hold and operate such a known screw driving gun with only one hand.
A further disadvantage arises in some of the known screw driving devices because the axis of the screwing bit is arranged a considerable distance above the axis of the drive motor. This position of the axis of the screwing bit is further away from the operator's hand than necessary, thereby producing a tilting moment during the screwing operation which may lead to an undesirable tilting of the screw itself whereby the screw is driven at an undesirable slant. Besides, the tilting moment causes an excessive fatigue on the operator's hand. Thus, in order to achieve an accurate screw position and to minimize fatiguing influences, known screw driving devices normally require to be held with both hands which is frequently inconvenient and not efficient.